Apparatus for forming an interference pattern of multiple indentations in the interior wall of conveying tubes

ABSTRACT

Apparatus, upon connection to a motive source, being selfadvancing in an auger-like manner for forming an interference pattern of multiple indentations in the interior wall of cylindrical conveying tubes, the pattern of indentations serving to eliminate streamer problems in tubes used to pneumatically convey plastic particulate material. The apparatus has an effective diameter greater than the inside diameter of the tube so as to spring and distort temporarily the tube from a cylindrical cross-section toward an elliptical cross-section, thereby using the inherent spring effect of the tube to provide force sufficient to form the indentations. The apparatus includes a pair of guide rolls and an indenting roll mounted on a support, the indenting roll having multiple teeth projecting from its periphery. The guide rolls are eccentrically displaced to one side of and at an oblique angle to the axis of the support, and the indenting roll is eccentrically displaced to the opposite side of the axis of the support and at an oblique angle opposite to that of the guide rolls. The effective diameter of the indenting roll including the projecting teeth is at least one half the inside diameter of a tube to be indented and is preferably of such diameter as to encompass the axis of the support.

XNTERFERENCE PATTERN OF MULTIPLE INDENTATIONS IN THE INTERIOR WALL OF CONVEYING TUBES [75] lnventorsi Bruce W. Stockbridge, Kingsport;

' Albert E. Spaller, Jr., Johnson City,

both of Tenn.

[73] Assignee: Eastman Kodak Company,

Rochester, N.Y.

[22] Filed: June 5, 1973 [21] Appl. No.: 367,300

[52] US. Cl 72/123, 72/112, 72/113, 302/64 [51] Int. Cl B21d 51/16 [58] Field of Search 72/112, 113,122, 123, A 72/78; 254/1345; 302/64 [56], References Cited UNITED STATES PATENTS 1,017,569 2/1912 Lewis 72/113 2,618,182 11/1952 Teetor 72/122 3,017,697 1/1962 Wlodek..... 72/113 3,029,668 4/1962 Wilman 72/123 3,117,821 1/1964 Mylting 302/64 Primary Examiner Lowell A. Larson I V i Attorney, Agent, or Firm-Malcolm G. Dunn United States Patent 1191 1111 3,824,827 Stockbridge et al. [4s] July'23, 1974 1 APPARATUS FOR FORMING AN 57 ABSTRACT Apparatus, upon connection to a motive source, being self-advancing in an auger-like manner for forming an interference pattern of multiple indentations in the interior wall of cylindrical conveying tubes, the pattern of indentations serving to eliminate streamer problems in tubes used to pneumatically convey plastic partic-u late material. The apparatus has an effective diameter greater than the inside diameter of the tube was to spring and distort temporarily the tube from a cylindrical cross-section toward an elliptical cross-section, thereby using the inherent spring effect of the tube to provide force sufficient to form the indentations. The apparatus includes a pair of guide rolls and an indenting roll mounted on a support, the indenting roll having multiple teeth projecting from its periphery. The guide rolls are eccentrically displaced to one side of and at an oblique angle to the axis of the support, and the indenting roll is eccentrically displaced to the opposite side of the axis of the support and at an oblique angle opposite to that of the guide rolls. The effective diameter of the indenting roll including the projecting encompass the axis of the support.

a .9l .m 5 Dra u moo D APPARATUS FOR FORMING AN INTERFERENCE ATTERN F MULTIPLEv INDENTATIONS IN TIIE INTERIOR wALL 0E CONVEYING TUBES BACKGROUND OF THE INVENTION This invention is directed to an apparatus for forming a pattern of multiple indentations in the surface of the interior wall of curved and straight sections of cylindrical conveying tubes or conduits employed in air or pneumatic conveying systems, which systems are adapted to move pelleted or particulate plastic material from one location to another while the material is suspended in the air or pneumatic stream, the indented surface serving in most instances to eliminate streamer problems.

Pelleted or particulate plastic material is often delivered in bulk form in railroad cars and is unloaded from the cars by air veying through tubes or conduits to storage silos, or from storage silos for movement from location to location in various manufacturing operations.

Manufacturing facilities handling such pelleted or particulate .pla'sticmaterial in the manner described, however, are confronted by .streamer problems. When the plastic pelleted material is moved in and by the air or other gaseous stream in the conveyingsysterns the pellets tend to rub against and abrade upon the otherwise relatively smooth interior walls of the tubes and conduits. Such abrading eventually results in the formation of a skin or smear, or plastic coating or filmbuild-up on such interior walls. Other pellets being conveyed, as a result of their abrasive action, cause peeling of such skins, smears or coatings from the interior walls in long, thin, narrow ribbons or streamers. These ribbons or streamers in turn tend to form aggregates or birds nests which clog or obstruct the free flow of the pellets in subsequent components of the conveying system, such as in the rotary feeders, valves, level indicators and collecting or storage hoppers. Centrifugal separators only become clogged when used in an attempt to separate the ribbons or streamers from the conveyed particulate material.

Different solutions havebeen proposed in an attempt to prevent such long ribbons or streamers.

One proposal involves employing a conveying tube or conduit that has provided substantially throughout the inner conduit wall shallow, rounded, helical or'transverse annular grooves or corrugations, as disclosed in the Fisher patent, U.S. Pat. No. 3,224,814, which issued Dec. 21, 4965. The internal corrugations or grooves are impressed on the inner wall of the conduit as by cutting or spinning on a lathe. If bends, curves of elbow sections in the conduit are required the lathe operation must be conducted first, and then the section undergoes a bending operation for formation of the bend, curve or elbow desired. A lathe operation is expensive, requires trained technical personnel and, of course, cannot be used on conduits that have already been formed into curved or elbow sections.

Another proposal involves forming uniform longitudinal serrations on the interior wall along the length of the conduit with the serrations being so dimensioned that the size particles conveyed through the conduit cannot contact the valleys between the ridges, as disclosed in the Scruby et al patent, U.S. Pat. No. 3,464,740, which issued Sept. 2, 1969. The serrations are formed when the conduit itself is extruded from aluminum. An extruding process involving serrations is also expensive, and would not be commercially practical for stainless steel conduits, for example, and obviously would not solve streamer problems for conduits already in existence.

Still another proposal involves providing a plurality of spaced protuberances arranged in spiral relation on the interior wall of the conduit for interfering with continuous sliding surface contact of the conveyed particulate material, as disclosed by the Hunter patent, U.S. Pat. No. 3,380,783, which issued Apr. 30, 1968. The protuberances are formed by use of a conventional die device for impressing the exterior surface of the tubular conduit section, the conduit being mounted upon an expansion mandrel. The operation is very slow and thus expensive time-wise. The expansion mandrel is first locked to hold the conduit section in the desied position; second, the die device is caused to impress the exterior surface for one protuberance; third, the mandrel is released so that the conduit may be rotated and advanced to the next desired position, and the entire operation is then repeated. Commercial use of conduits having such protuberances, however, has not elimihated the streamer problem.

, A further proposal involves providing triple grooves and ridges extending along-the grooves in a helical generation on the interior wall of the conduit, as disclosed in the Mylting patent, U.S. Pat. No. 3,117,821, which issued Jan. 14, 1964. The grooves and ridges are formed by a device that has three small mounted tools angularly disposed at from each other and axially spaced apart a predetermined distance. The mounted tools serve to form the grooves by causing a flow of the metal rather than by causing a cutting action. The flowing action causes the metal to be pushed to either side of the grooves simultaneously forming the ridges. The theory of operation is conveying particulate material in a conduit treated in this manner is that the particles that would otherwise tend to smear along the interior wall are continually deflected toward the axis of the conduit and in the downstream direction of axial flow by the triple groove formation.

A stillfurther proposal involves producing a roughened interior wall surface by sand blasting, as disclosed in the Schneider patent, U.S. Pat. No. 2,784,038, which issued Mar. 5, 1957. The apparent theory of operation is that roughening the interior wall surface of the conduit will tend to create turbulence in the air stream flowing through the conduit and thus reduce the tendency of the plastic particulate material to be deposited in the form of a layer or skin on the interior wall. In practice the toughening tends after a time to become obliterated by the abrasive effect of the particulate material which constantly impinges upon the interior wall of the conduit tube, thereby requiring the sandblasting operation to be repeated from time to time. Dismantling and handling conduit sections for each sandblasting operation is time consuming and expensive. The roughened surface, which has the feel and appearance of sandpaper, appears also to produce more fines or dust particles due to the abrading action between the conveyed particles and the roughened surface.

A more suitable solution to the streamer problem, however, is proposed in U.S. Pat. application Ser. No. 730,799, which was filed May 21, 1968, in the name of Garland B. Keith and subsequently abandoned in favor of pending continuation application Ser. No. 275,122, filed July 26, 1972. This solution involves the concept of providing a conveying tube with patterned indentations in the interior wall of conveying tubes. The solution is more suitable from a commercial point of view for a number of reasons. The indentations can be formed by a relatively small tool or apparatus that is inexpensively produced, by comparison to lathe'equipment, for instance, and that does not require skilled technical personnel to operate. The tool or apparatus can be used on new conveying tubes or on previously installed conveying tubes, and on tubes that have already been formed into smooth radius curves and elbows. The tool or apparatus only requires a few minutes to treat a section of conveying tubing that may be or feet in length. The length of tubing that may be treated in its installed conveying position is limited only by what is considered to be the practical length drive arrangement that may be connected to the tool. The indentations have little or no effect on the pelleted material being conveyed through the tube. The indentationsare of smaller dimensions than the pelleted ma-' terials and anyabrasion of the pelleted material would appear to be minimal because, in most instances, depending upon the type of material conveyed, there does not appear to be any increase in fines or dust particles over that produced in untreated tubes. In some instances, there were fewer fines.

Each indentation results in a gap or interruption in the otherwise smooth interior wall of the tube. If the conveyed particulate material should form a film-like build-up due to rubbing or abrading against the tube interior wall surface, subsequent abrasion by other conveyed particulate material only results in the film-buildup flaking off in segments the lengths of which are determined by the distance from one indentation-to the next indentation in'alignment with the flow path of the conveyed material. This distance, for practical purposes, has been found to be about one eighth to one quarter inch. Any segments that may flake off will be in corresponding lengths,'-and thus there would be'no long streamers or ribbons produced that could clog conveying and otherequipment. v

The pending Keith patent application discloses a workingembodiment of a tool or apparatus for forming a pattern of indentations in a desired manner. The tool or apparatus has an indenting roll and a pair of guide rolls that are canted in such manner as to make the tool self-advancing in an auger-like manner. The indenting roll is adjustably spring-biased to assure continuous contact between the tube and indenting roll, to provide substantially constant tool pressure, and to control the maximum depth of the indentations.

Although the tool or apparatus disclosed in the pending application maybe used in conveying tubes made of varying materials, metals, plastics and the like, the working life of the apparatus in certain harder materials such as of stainless steel has proved to be relatively short due to breakage of the teeth of the indenting roll. Also the harder tube materials, depending also upon the gauge and strength of the material, make it more difficult for the apparatus to perform effectively since in some instances as on smaller internal diametered tubes it is not possible to provide springs or other force applying expediencies sufficiently strong to maintain constant tool pressure. A Spring is usually a more practical mechanical expediency to use because it enables the tool it is biasing to adapt itself to most variations in the internal contour of conveying tube. It is not essential that a conveying tube be precisely round in crosssection, hence the tube is often just generally round. The tube is handled in sections before assembly, and in the course of assembly, for one reason or another, the tube will often be out-of-round in places. I

In effectively and uniformly indenting the harder material, therefore, such as a stainless steel tube having an outside diameter of about 5 inches and having walls that are about 1 l to 16 gauge, the force required to indent is on the order of about 4,000 to 6,000 pounds. It is not practical to employ a spring large enough to bias the tool or apparatus for making the indentations. Other mechanical expediencies, which may be suitable,

when adjusted to urge the indenting roll to conform to a desired dimension within the conveying tube, can not adapt for out-of-roundness and weld joints.

As will become evident from the disclosure set forth hereinafter, the present invention provides a simple, effective and relatively inexpensive means for prevention and elimination of the above-described streamers or ribbons of plastic material in pneumatic conveying tubes and the like by a tool that may be used not only on straight sections of conduit or conveying tubes but also on curved and elbow sections, which tubes may be made of aluminum, stainless steel, plastic or of other suitable materials. More significantly, the tool or apparatus is adapted to take advantage of the potential spring effect in the conveying tube itself in achieving the desired indenting force for uniform treatment of such conveying tubes, and for maintaining continuous contact between the indenting roll of the apparatus and SUMMARY OF THE INVENTION The present invention is directed to an apparatus for forming in the interior wall of a cylindrical conveying tube an interference pattern of multiple'indentations. The pattern interferes with the formation of long streamers which would otherwise occur when film build-up on the interior wall surface from the conveyed particulate material is caused to peel/away from the wall surface as streamers along-indefinite length paths that are generally parallel to the longitudinal axis of the tube and of the pneumatic flow path. Thus whatever film build-up occurs in the course of conveying plastic particulate material, the abrasion by other particulate material will only cause the film build-up to flake away in short segments. The length of each short segment represents the distance between indentations lying along the same path of pneumatic flow, which is also the same path that is generally parallel to the conveying tube axis. The distance, dependent upon the design of the apparatus, being about one eighth to about one quarter inch. In other words, in the manner in which the apparatus operates the conduit tube interior wall along its surface will have no uninterrupted straight line paths which would otherwise enable the formation of long streamers or ribbons.

The concept of the conduit tube with the indentations and the method for forming such is the subject of pending U.S. patent application Ser. No. 730,799, filed May 21, 1968, in the name of Garland B. Keith, now

abandoned in favor of pending continuation application Ser. No. 275,122, filed July 26, 1972. i

The apparatus is adapted to be self-advancing in auger-like manner through the conveying tube upon being driven in rotation by connection to a motive source. The effective diameter of the apparatus is predeterminedly greater than the inside diameter of the conveying tube so that as the apparatus moves through the tube the tube, in the area of and at the time of contact with the tube by the apparatus, is sprung and distorted temporarily from a cylindrical cross-section toward an elliptical cross-section. The elasticity of the cylindrical tube serves to provide force sufficient for forming the indentations. The apparatus thus utilizes the inherent spring effect formed by the tube itself upon being temporarily distorted. In this manner the apparatus is not hampered by the necessity to employ large compression springs or other force applying mechanical expediencies, which otherwise would be required in indenting stainless steel conveying tubes, for instance.

The apparatus comprises a support for an indenting roll and a pair of guide rolls. The guide rolls are mounted in spaced relation from each other on and along the lengthof the support; they lie in separate parallel oblique planes with respect to the axis of the support; and they are eccentrically displaced in one direction from the axis of the support. The indenting roll is mounted on the support between thepair of guide rolls and lies in a separate oblique plane that slants to the same extent as the guide rolls but in the opposite direction from the direction toward which the guide rolls are slanted. The indenting roll is also eccentrically displaced from the axis of the support in the opposite direction from the eccentric displacement of the guide rolls and has a plurality of teeth or tool bits projecting from its peripheral surface for forming the indentations.

The effective diameter of the indenting roll, including the distance to which the teeth or projecting tool bits extend beyond the peripheral surface of the roll, is at least one-half the inside diameter of the conveying tube to be indented but is less than theinside diameter of the tube, and preferably has an effective diameter that ecompasses the axis of the supportas the guide rolls and indenting roll move together along the axis of the coneying tube with the rolls tracing a helical path around the interior wall of the conveying tube at a constant distance from the axis of the tube.

The effective diameter of the apparatus represents the distance from the point of tangency of the guide roll peripheral surface, where it is in engagement with the interior wall on one side of the tube, to the tip of the farmost indenting roll tool bit or tooth that is, at the point of tangency, where it will be in indenting engagement with and into the desired depth in the interior tube wall at the opposite side of the tube from the guide roll engagement,'when the apparatus is operated in a particular size of tube. The effective diameter, therefore, is the inside diameter D of the tube plus A D, the additional distance beyond diameter D calculated to provide the desired distortion of the tube toward an elliptical cross-section in producing the desired depth of the indentation to be made.

The guide rolls and the indenting roll are adapted by their positions onthe support so that the guide rolls simultaneously engages one side of the tube interior wall and the indenting roll engages the opposite side of the tube interior wall.

The effective diameter of the indenting roll is significant in that the teeth or tool bits follow a path into and out of indenting engagement with the interior wall in such manner that the force on each tool bit is more in compression than in shear or bending. In this manner lateral or side thrust is minimized and thus there is less likelihood of the tool bits breaking at their tips when used on conveying tubes made of hard material such as stainless steel. Also, the greater the effective diameter of the indenting roll with respect to the inside diameter of the conveying tube the less force required to rotate the apparatus because the unit load is spread over a larger area.

The effective diameter of the guide rolls is significant for one of the same reasons applicable to the indenting roll: to spread the unit load over a larger area thereby resulting in less force required to rotate and move the apparatus through a conveying tube.

The effective diameters of the guide and indenting rolls thus facilitate the operation of the .apparatus and result in formation of relatively clean indentations, minimizing the formations of any rough projections from the interior wall surface of the conveying tube. The apparatus is readily worked in hard materials, such as stainless steel, as well as in softer materials such as aluminum and plastic. Elbow bends and curves in conveying tubes may also be treated by the apparatus.

The guide rolls are provided with crowned crosssections so that the leading edges extend below or inwardly of the lip of a conveying tube to enable initial entry by camming into a conveying tube without the necessity of clamping the tube to squeeze it toward an elliptical cross-section in order to get the greater diam etered apparatus into the smaller inside diameter opening of the tube.

BRIEF DESCRIPTION 0F THE DRAWINGS In the drawings:

FIG. 1 is an elevational view of an indenting apparatus positioned in operative relation within a cylindrical conveying tube with the tube being shown in crosssection and distorted by the apparatus which has an effective diameter greater than the inside diameter of the tube; FIG. 2 is a view similar to FIG. 1 but illustrating the appearance of the tube when the apparatus has been rotated to a position from the position of the apparatus in FIG. 1;

FIG. 3 is an enlarged isometric view of the indenting apparatus within a conveying tube with a portion of the apparatus and tube cut-away and in cross-section, and also illustrating the indentations that have been made in the interior wall of the conveying tube;

FIG. 4 is an enlarged end view in cross-section of a conveying tube distorted toward an elliptical crosssection, showing an indenting roll that is greater than one-half the inside diameter of the conveying tube, and illustrating the greater angle over which the indenting roll is engaged with the interior wall of the tube, the lines of force and the small angle between the lines of force; and

FIG. 5 is a view similar to FIG. 4 but showing an indenting roll that is less than half the inside diameter of the conveying tube, and illustrating the smaller angle over which the indenting roll is engaged with the tube and the related lines of force and larger angle between the lines of force.

In reference to the drawings, 10 designates a portion of a conveying tube, 12 the indenting apparatus, and 14 a portion of a motive source such as a flexible power shaft (FIG. 3) that may be connected to the apparatus and driven by an electric or. air motor.

The indenting apparatus comprises a support 16, a pair of guide rolls 18 and 20, an indenting roll 22 and a connecting structure 24 for making a suitable drive connection with the motive source 14. A plurality of teeth or tool bits 26 project from the periphery of the indenting roll for forming indentations.

The support 16, although shown in FIG. 3 as being machined from one piece of metal stock, may also be made in several sections and suitably secured together. Journals 28, 30, 32 are formed, respectively, for the guide roll, indenting roll 22 and guide roll 20, eccentric to and at oblique planes with the axis of the support.

Each roll is provided with a ball hearing, as shown in FIG. 3 at 34, 36 and 38, which along with the rolls are mounted'upon the respective journals and suitably secured to the support.

A series of holes 40 are bored into the periphery of the indenting roll, the holes being of such diameter as to provide a friction fit for each tool bit 26. The peripheral surface of ball bearing 36 serves to support the bottom of each tool bit .or tooth. This manner of construction facilitates replacement of the individual tool bits in the event of breakage or dulling or for whatever reason.

The tooth 26, as shown in the cut-away position of the indenting roll in FIG. 3, is a cylindrical rod of hard material such as a tool bit of tungsten carbide. Although the configuration of the indentation made by the tool bit may take various forms, the form shown in the drawing (FIG. 3) is made by chisel shaped teeth, as shown at 42. This form is thought to provide more resistance to possible tooth breakage in hard materials.

Each guide roll 18, 20, is provided with a crowned cross-section, as shown, for instance, at 44 in FIG. 3. Since the effective diamete'r'of the apparatus is greater to a predetermined extent than the inside diameter of the conveying tube, thev crownis designed so that the leading edges of the guide rolls extend below or inwardly of the lip of the conveying tube to facilitate introduction of the apparatus by camming smoothly into the conveying tube. The curved crown also serves to eliminate the possibility of scoring the interior wall by the peripheral edges of the guide rollsfSuch scoring would otherwise present jagged surfaces extending from the tube interior wall that might unnecessarily produce more fines by abrading the conveyed material.

As heretofore mentioned, the effective diameter of the apparatus represents the distance from the point of tangency of the guide roll peripheral surface, where it is in engagement with the interior wall on one side of the tube, to the farmost tip of the indenting roll tool bit or tooth that is at the point of tangency, where it will be in indenting engagement with and into the desired depth in the interior tube wall at the opposite side of the tube from the guide roll engagement, when the apparatus is operated in a particular size of tube. The effective diameter, therefore, is the inside diameter D of the tube plus A D, the additional distance beyond diameter D calculated to provide the desired distortion of the tube toward an elliptical cross-section in producing the desired depth of the indentation to be made.

In the example of a 300 Series Stainless Steel conveying tubing having the following dimensions:

an apparatus having the following dimensions was employed: I

Apparatus =4.863 inches Effective Diameter Indenting Roll =4452 inches Effective Diameter Guide Roll Effective Diameter =4.500 inches Displacement of =0.2OO inch Indenting Roll from Support Axis Displacementof =0.l87 inch Guide Rolls from Support Axis Lead Angle for Guide and lndenting Rolls AD therefore is =0.l03 inch the tool bits or teeth extend beyond the peripheral surface of the roll. The effective diameter of the indenting roll, when mounted on the support 16, is at least one half the diameter of the tube to be indented, and preferably is of such diameter as to encompass the axis of the support. Thus the diameter of the indenting roll approaches the inside diameter of the tube to be indented but does not exceed such inside diameter. The purpose of the larger diametered indenting roll is to spread the force applied by the indenting roll against the tube over a greater area or angle of contact. In'this mannerthe force placed on the tool bits will be more in compression than in shear or bending which would otherwise tend to break the tips of the teeth.

In reference to FIGS. 4 and 5, these figures illustrate the difference in contact or tube engagement angle between an indenting roll 22 having an effective diameter of 4.863 inches (FIG. 4) and an indenting roll 22 having an effective diameter of about 2.400 inches when used with a tube having an outside diameter of about 5 inches. In FIG. 4 the contact angle A is about 845 whereas in FIG. 5 the contact angle A is about38.0. LOFI in FIG. 4 designates the line of force on the indenting roll 22 and LOFT designates the line of force on the conveying tube 10. LOFI' and LOFT in FIG. 5 designate similar lines of force applicable to indenting roll 22' and conveying tube 10.

As the angle B (FIG. 4), B (FIG. 5) between the line of force on the indenting roll and the lineof force on the conveying tube decreases, the mechanical advantage increases, thereby reducing the torque required to be applied to the indenting roll to achieve rotation for a given contact angle, and therefore reduces the tangential or lateral load on the tool bits. The less lateral the load or side thrust, especially in hard materials, the less tendency for the tool bits to twist or roll over or break at their tips. FIG. illustrates, of course, a greater increase in angle B, and hence more torque would be required to rotate the apparatus.

The advantage represented by an apparatus having the larger diametered indenting roll whereby less torque is required to rotate the apparatus is further enhanced by employing guide rolls which also have a greater diameter, as shown in FIGS. 1 through 3.

In the apparatus, the guide rolls 18, are positioned on the support 16 at an oblique angle, and are also eccentrically displaced from the axis of the support. The indenting roll 22 is similarly positioned on the support at an oblique angle in the direction opposite to the direction shown by the guide rolls and eccentrically displaced from the axis of the support, also in a direction opposite to that of the guide rolls.

In the apparatus illustrated and for a tube having an outside diameter of 5 inches, the oblique angle 0A (FIG. 2) for the guide and indenting rolls selected is about which also represents the lead angle for the guide rolls which are thus adapted to self-advance the apparatus in a helical path or auger-like manner around and along the length of the conveying tube. The lead angle will vary depending on factors such as the inside diameter of tube, spacing and number of tool bits, amount of advance desired, and the like.

, OPERATION apparatus to move into proper position so that the axisof the upport 16 is then placed in general alignment with the axis of the tube. The crowned cross-section of the guide rolls facilitates such introduction of the apparatus, as; previously mentioned.

Each roll rotates in a circle eccentric to the axis of the support while tracing at its peripheral surface a helical path on the interior wall of the conveying tube, the path extending radially outwardly to a diameter greater than the normal inside diameter of the tube. The tube, therefore, must remain free to be expanded or distorted from a generally cylindrical cross-section toward an elliptical cross-section in the area of and at the time of contact by the apparatus with the tube. As shown in FIG. 1 the wall of the tube is distorted radially outwardly, while FIG. 2 illustrates the apparatus in a different attitude of rotative orientation which causes the portion of the tube wall out of engagement with the rolls to be drawn radially inwardly. The outward appearance of the tube one sees in observing the apparatus in operation is like a pulsing or wave-like action. The force of the outward, and inward movement of the tube wall results information of the indentations as the apparatus moves through and along the length of the conveying tube.

The indentations may either be formed during a single pass of the apparatus with the apparatus being disconnected from its drive source for removal from the tube upon completion of a section of tube, or the apparatus may be moved in rotation back through the tube section resulting in additional indentations being formed as different helical paths are traced by the rolls.

In the manner disclosed the apparatus readily forms indentations in hard materials as well as the softer materials, and including any weld joints that may have been used in forming the tube or joining tube sections together.

The invention has been described in detail with particular reference to preferred embodiments thereof,

' being driven in rotation by connection to a motive source and having an effective diameter predeterminedly greater than the inside diameter of the conveying tube so that as the apparatus moves through the tube the tube in the area of and at the time of contact with the tube by the apparatus is sprung and distorted temporarily from a cylindrical cross-section toward an elliptical cross-section, the elasticity of the cylindrical tube serving to provide the force sufficient for forming the indentations, the apparatus comprising:

support means;

means connected to the support means and when connected to a motive source adapted for driving the support means in rotation;

a pair of guide rolls mounted in spaced relation from each other on and along the length of the support means and lying in separate parallel oblique planes with respect to the axis of the support means, the guide rolls being eccentrically displaced in one direction from the axis of the support means; and

an indenting roll mounted on the support means be tween the pair of guide rolls and lying in a separate oblique plane that slants to the same extent as the guide rolls but in the opposite direction from the direction toward which the guide rolls are slanted, the indenting roll being eccentrically displaced in the opposite direction from the eccentric displacement of said guide rolls and having means projecting from the peripheral surface of the indenting roll for forming indentations in the conveying tube, the effective diameter of the indenting roll being at least one-half the inside diameter of the conveying tube to be indented but less than said internal diameter;

the guide rolls and the indenting roll thereby being adapted by their positions on the support means so that the guide rolls simultaneously engage at one side of the interior wall of the tube and the indenting roll engages at the opposite side of the interior wall, and upon the support means being driven in rotation the guide rolls, the indenting roll and support means are moved together along the axisof the conveying tube with the guide rolls and indenting roll tracing a helical path around the interior wall of the conveying tube at a constant distance from the axis of the cylindrical tube.

2. An apparatus as defined in claim 1, and wherein the effective diameter of the guide rolls is at least onehalf the inside diameter of the conveying tube to be indented but less than said inside diameter.

3. An apparatus as defined in claim 1, and wherein the engaging surface of each guide roll has a crowned cross-section across the width thereof, the leading edge of the-crown extending below or inwardly of the lip of the tube to be indented.

means. 

1. An apparatus for forming in the interior wall of a cylindrical conveying tube an interference pattern of multiple indentations, the apparatus adapted to be self-advancing in auger-like manner through the tube upon being driven in rotation by connection to a motive source and having an effective diameter predeterminedly greater than the inside diameter of the conveying tube so that as the apparatus moves through the tube the tube in the area of and at the time of contact with the tube by the apparatus is sprung and distorted temporarily from a cylindrical cross-section toward an elliptical cross-section, the elasticity of the cylindrical tube serving to provide the force sufficient for forming the indentations, the apparatus comprising: support means; means connected to the support means and when connected to a motive source adapted for driving the support means in rotation; a pair of guide rolls mounted in spaced relation from each other on and along the length of the support means and lying in separate parallel oblique planes with respect to the axis of the support means, the guide rolls being eccentrically displaced in one direction from the axis of the support means; and an indenting roll mounted on the support means between the pair of guide rolls and lying in a separate oblique plane that slants to the same extent as the guide rolls but in the opposite direction from the direction toward which the guide rolls are slanted, the indenting roll being eccentrically displaced in the opposite direction from the eccentric displacement of said guide rolls and having means projecting from the peripheral surface of the indenting roll for forming indentations in the conveying tube, the effective diameter of the indenting roll being at least one-half the inside diameter of the conveying tube to be indented but less than said internal diameter; the guide rolls and the indenting roll thereby being adapted by their positions on the support means so that the guide rolls simultaneously engage at one side of the interior wall of the tube and the indenting roll engages at the opposite side of the interior wall, and upon the support means being driven in rotation the guide rolls, the indenting roll and support means are moved together along the axis of the conveying tube with the guide rolls and indenting roll tracing a helical path around the interior wall of the conveying tube at a constant distance from the axis of the cylindrical tube.
 2. An apparatus as defined in claim 1, and wherein the effective diAmeter of the guide rolls is at least one-half the inside diameter of the conveying tube to be indented but less than said inside diameter.
 3. An apparatus as defined in claim 1, and wherein the engaging surface of each guide roll has a crowned cross-section across the width thereof, the leading edge of the crown extending below or inwardly of the lip of the tube to be indented.
 4. An apparatus as defined in claim 1, and wherein the effective diameter of the indenting roll encompasses the axis of the support means as the indenting roll is moved in its helical path.
 5. An apparatus as defined in claim 1, and wherein the effective diameter of the guide rolls encompasses the axis of the support means.
 6. An apparatus as defined in claim 1, and wherein the effective diameters of the guide rolls and of the indenting roll each encompass the axis of the support means. 